The need for a clean energy source has stimulated much effort in pursuit of hydrogen-based fuel-cell technologies. Obstacles to solving this problem have been the lack of practical systems for hydrogen storage and an inability to identify the key factors that promote optimal hydrogen storage. Adsorbents derived from carbonaceous materials have been widely studied, but do not yet meet all the requirements for hydrogen storage capacity, cost, and ease of manufacturing.
It has proved difficult to prepare carbon samples with high surface areas (1,500-3,000 m2/g) from a wide variety of carbonaceous precursors. Previous approaches typically involved pyrolysis in either an oxidizing atmosphere (e.g., air) or an inert atmosphere (e.g., nitrogen). Previously disclosed hydrogen treatment processes were conducted at lower temperatures (50-400° C.), and were designed to remove impurities on the surface of fullerenes, carbon nanofibers, carbon nanotubes, carbon soot, nanocapsules, bucky onions, carbon fibers and other carbonaceous material
Shiraishi et al. (US2003/0118907) disclose a hydrogen-storing carbonaceous material obtainable by heating a carbonaceous material in a gas atmosphere including hydrogen gas and substantially including no reactive gas as impurity gas.
Wojtowicz et al. (US2002/0020292) disclose a method for storing gas by carbonizing a carbonaceous precursor material in a substantially nonoxidizing atmosphere and at temperatures that attain an upper value of at least 1000° C. (to produce substantial graphitization of the carbon of the precursor material) and then introducing a gas (e.g., hydrogen) to be stored, under positive pressure, into a storage vessel containing a substantial amount of the sorbent material.
Wojtowicz et al. (Int. J. Soc. Mat. Eng. Resources, Vol. 7, No. 2, 253-266 (1999)) disclose the char-activation of polyvinylidene chloride to form a hydrogen storage material with high micropore volumes. No data is provided on the structural characterization (i.e., crystallinity or presence of turbostratic regions) of these materials.
Rodriquez et al. (U.S. Pat. No. 5,653,951) disclose a solid layered nanostructure comprised of crystalline regions, interstices (0.335 nm to 0.67 nm) within the crystalline regions, and nanostructure surfaces defining the interstices which have hydrogen chemisorption properties. A composition comprising the solid layered nanostructure with hydrogen stored in the interstices is also disclosed.
Nijkamp et al. (Appl. Phys. A 72, 619-623(2001)) and Chahine et al. (Hydrogen Energy Progress XI, Proceedings of the World Hydrogen Energy Conference, 11th, Stuttgart, Jun. 23-28, 1996, Vol. 2, 1259-1263) tabulate the hydrogen adsorption capacity, pore volumes and surface areas of several carbonaceous materials. No data is provided on the structural characterization (i.e., crystallinity or presence of turbostratic regions) of these materials.
Quinn et al. (U.S. Pat. No. 5,071,820) disclose a process for activating carbon to produce a carbon having a high micropore and low macropore volume by a series of steps of heating the carbon in the presence of oxygen, followed by heating the carbon in a nitrogen atmosphere. No data is provided on the structural characterization (i.e., crystallinity or presence of turbostratic regions) of these materials.
In the last several years, much effort has been made to understand the characteristics of carbon adsorbents that correlate with high storage capacity. Materials with high hydrogen storage capacity are of special interest. Nijkamp and others have observed that surface area seems to be a key factor for hydrogen storage, but it is clearly not the only one, since there is a great deal of scatter in the data for samples with moderate surface areas (1,000-1,500 m2/g). Based on data obtained for these moderate surface area carbons, it has also been proposed that micropore volume is another key factor, even though the hydrogen adsorption data is also badly scattered for this variable.